Data transmission over an optical medium such as an optical fiber typically requires use of a laser classified by the limit imposed on output power (and the corresponding danger associated with use of such output power), with many systems employing, for instance, a Class 2 laser. Accordingly, the output power of lasers employed must satisfy stringent eye safety requirements and equally stringent requirements defined by the transmission protocol (e.g., Ethernet, fiber channel, etc.).
Conventional optical power control schemes employ a p-type/intrinsic/n-type (PIN) semiconductor light detection monitor diode and a partially reflective lens to monitor the output of a vertical cavity surface emitting laser (VCSEL) or other light source. A small fraction of the light emitted by the laser is reflected to the PIN diode, which converts the light to an electrical current sensed by a transimpedance amplifier for conversion into a voltage. The voltage representative of the reflected light is compared against a reference voltage and an error signal generated on the basis of that comparison is employed to servo the VCSEL light output power to desired level.
Use of a complex lens to partially reflect transmitted light onto a monitor diode employed to control output power introduces mechanical and optical design complexities and assembly complexity, and increases costs. In addition, detailed knowledge of the package design and/or VCSEL characteristics is typically required.
There is, therefore, a need in the art for a system and technique for monitoring output power from a data transmission light source without requiring use of a monitor diode.